The present invention pertains to a coating applied by chemical vapor deposition (CVD) and coated products, especially coated cutting inserts that are useful in material removal applications such as, for example, machining, turning, and milling. More specifically, the present invention pertains to a coated body, such as, for example, a coated cutting insert, wherein the coating scheme includes a coating layer of alumina and a titanium-containing material (e.g., titanium carbonitride and/or titanium aluminum oxycarbonitride) whereby the coating layer, which is applied by CVD, has acceptable adhesion and abrasive wear resistance, and methods of making the coating and the coated body.
Heretofore, coated bodies, such as, for example, coated cutting inserts, have been used in material removal applications. The coating layers typically comprise hard refractory materials that exhibit the property of wear resistance. One primary purpose of using a coating on a cutting insert has been to lengthen the useful life of the cutting insert. There have been coating schemes that include a coating layer of alumina and/or titanium carbonitride, and exemplary ones of these coating schemes are described in some of the following patent documents.
United States Published Patent Application No. US2003/0008181 A1 to Ljungberg pertains to a coated cutting tool that has an alumina coating with fine, equi-axed grains. U.S. Pat. No. 4,984,940 to Bryant et al. and European Patent No. 0 463 000 B1 each disclose using thin layers of a nitride of titanium, zirconium and/or hafnium to separate alumina layers wherein it includes a process of interrupting the deposition of a coating material. Published U.S. Patent Application No. US2002/0122701 A1 to Ljungberg et al. discloses that non-columnar alumina can be deposited via interrupting the deposition of the alumina.
U.S. Pat. No. 5,700,569 to Ruppi discloses a coating scheme comprising a plurality of alumina layers. If the alumina is kappa-alumina, there is a “modification layer” deposited on the surface of the underlaying alumina layer wherein the modification layer may comprise (Al Ti) (O,C,N).
European Patent No. 0980917 B1 to Toshiba Tungaloy discloses a coating scheme that comprises TiN/Ti(C,N)/(Ti,Al)(C,N,O)+Al2O3/Al2O3/TiN. U.S. Pat. No. 5,545,490 to Oshika pertains to a coated cutting tool that includes a coating sequence that comprises TiN/TiCN/TiCNO/Al2O3. The TiCNO layer is a thin layer that separates the TiCN from the alumina layer. PCT Patent Application No. WO 99/58738 to Valenite, Inc. discloses a cemented carbide or ceramic article that presents a multi-layered CVD coating. In one embodiment, the coating comprises a layer of titanium carbonitride near the surface of the cemented carbide substrate, a multi-layered coating structure of alternating ultrathin layers of titanium carbonitride and alumina, and an outer layer of titanium nitride.
U.S. Pat. No. 4,714,660 to Gates, Jr. pertains to hard coatings on a cemented carbide substrate. The coating may comprise titanium-aluminum oxycarbonitride (TiwAlxOyCzNu) where w, x, y, z and u represent the mole fractions of Ti, Al, O, C and N, respectively. Published United States Patent Application No. US2002/0176755 A1 to Ruppi shows multiple alternating layers of MT-TiCN and alumina (Kappa phase and gamma phase). U.S. Pat. No. 6,333,099 B1 to Strondl et al. pertains to alternating coating sequences that contain alumina and what may be a titanium-aluminum carbide or nitride.
PCT Patent Application No. WO99/29920 to Sandvik A B and PCT Patent Application No. WO99/29921 each concern a periodic coating scheme in which alumina is one of the alternating coating layers. The other layer is a carbide or a nitride wherein the metals (M and L) can include Ti and Al. PCT Patent Application No. WO00/52225 to Kennametal for A TOOL HAVING A MULTILAYER COATING COMPRISING MULTIPLE MTCVD LAYERS discloses multiple layers of MTCVD-applied material separated by an interposed layer.
U.S. Pat. No. 5,700,551 to Kukino et al. discloses a modulated coating layer. FIG. 4 presents a periodic change in the coating composition. European Patent No. 0 709 483 B1 to Sumitomo Electric Industries pertains to a coating scheme that presents a compositionally modulated region. FIG. 17 depicts a modulated coating scheme.
U.S. Pat. No. 5,330,853 to Hofmann et al. pertains to a TiAlN coating scheme. The layers differ in the nitrogen content and a nitrogen gradient is shown through the thickness of a coating layer. U.S. Pat. No. 5,436,071 to Odani et al. and U.S. Pat. No. 5,920,760 to Yoshimura et al. disclose MT-CVD TiCN coatings. European Patent No. 1 026 271 B1 to Sandvik A B (Palmqvist et al. inventors) discloses cemented carbide (WC—Co plus additives) inserts that have the following coating sequence: TiN/MT-TiCN/α-Al2O3/TiN. U.S. Pat. No. 4,028,142 to Bitzer et al. and U.S. Pat. No. 4,196,233 to Bitzer et al. disclose methods for making MTCVD coatings.
U.S. Pat. No. 5,164,051 to Komaki et al. relates to the pre-coating preparation of a substrate surface. These steps include electrolytically polishing the surface and scratching the surface. The substrate can be WC—Co and the coating is diamond. U.S. Pat. No. 5,380,408 to Svensson pertains to etching to remove cobalt from the surface of a substrate, as well as mechanical treatments such as blasting. U.S. Pat. No. 6,110,240 to Saguchi et al. discloses a pretreatment of the substrate prior to diamond coating. U.S. Pat. No. 5,648,119 to Grab et al. discloses (Col. 11, lines 55-58) buffing the diamond coated substrate.
As is apparent from the above documents, many different coating schemes for a coated cutting insert have been used in the past. According to these patent documents, each one of these coating schemes provides certain advantages. Even though there have been coating schemes that are supposed to provide certain advantages, there has always remained a desire to continue to lengthen the useful life, as well as to improve the performance characteristics, of the coated cutting inserts.
The desire to lengthen the useful life and improve the performance characteristics is especially the case for coated cutting inserts that use alumina and/or titanium carbonitride coating layers applied by CVD since these materials have good wear resistance properties. Alumina coating layers include refined grain alumina coating layers that exhibit excellent abrasion assistance. The same is true for titanium carbonitride coating layers including fine grain titanium carbonitride coating layers in that these coating layers exhibit excellent abrasion resistance. In the context of and for the purpose of this description and the claims, a refined grain microstructure is considered to exhibit an average grain size equal to or less than about one micrometer. However, one drawback with these coatings has been that when one deposits a thicker coating the grain structure becomes coarser as the thickness of the coating increases. A coarser grain structure typically reduces the abrasion resistance so that thicker coatings of alumina and/or titanium carbonitride have not provided for improved abrasion resistance.
Thus, it would be highly desirable to provide an improved coated cutting insert wherein the CVD coating comprises a coating scheme that includes a coating layer of alumina and a coating layer of titanium-containing material (e.g., titanium aluminum oxycarbonitride and/or titanium aluminum carbonitride) and the cutting insert is useful in material removal applications wherein the cutting insert has a lengthened tool life, as well as exhibits improved performance characteristics.